Valve-regulated lead acid (VLRA) batteries, commonly referred to as sealed batteries, are rechargeable batteries that can be mounted in any orientation. Unlike conventional flooded cell batteries, which use liquid, aqueous sulfuric acid as an electrolyte, VRLA batteries primarily include gel cell and Absorbed Glass Mat (AGM) battery types. In a gel cell battery, the sulfuric acid electrolyte is immobilized in a gel form. In an AGM battery, a fiberglass mat is impregnated with the aqueous sulfuric acid electrolyte, which retains the absorbed electrolyte through capillary action.
Generally, when a battery cell discharges, lead-sulphate and water are produced as the lead and sulfuric acid undergo a chemical reaction. When the battery cell is subsequently charged, the lead-sulphate and water are converted back into lead and sulfuric acid. During the charging process, and especially under extreme conditions, hydrogen and oxygen gasses are created. To prevent damage to the battery cell, VRLA batteries have pressure release valves positioned in the battery cover. These pressure relief valves activate when internal pressure exceeds a predetermined level, venting hydrogen and oxygen gas.
In FIG. 1, a conventional pressure releasing valve assembly 10 is shown. The assembly 10 includes a body 11 having a flange 12 on a first end 11a, a threaded portion 13 on a second end 11b, and a receiving passageway (not shown) extending through the body 11 from the first end 11a to the second end 11b; and a pressure relief valve 14 positioned over the first end 11a of the receiving passageway 14. When installed on a VRLA battery cover (not shown), the threaded portion 13 is screwed into a complimentary valve assembly receiving space (not shown) disposed on the cover.
While the conventional pressure releasing valve assemblies 10 work effectively under normal operating conditions, batteries using the convention assembly 10 do not always pass IATA/DOT vibration testing, described in Battery Counsel International Standard BCIS-21. Under the IATA/DOT vibration test, the battery is subjected to significant levels of vibration in three orientations, whereby the battery must remain leak-free during the entire process. Typically, the conventional pressure releasing valve assembly fails in the inverted orientation, where electrolyte leakage is observed. Consequently, conventionally equipped VRLA batteries are not always permitted to be classified as IATA/DOT approved, meaning they are classified as dangerous materials, severely restricting air transport and subjecting them to hazardous materials regulations.
There is a need for a pressure releasing valve assembly that will permit a thus equipped VRLA battery to pass the IATA/DOT vibration test.